A 54 amino acid paralytic peptide named soricidin (NCBI accession no. P0C2C6) was discovered and isolated from the submaxilary saliva gland of the Northern Short-tailed Shrew (Blarina brevicauda). A previous patent on the use of soricidin in treating pain (U.S. Pat. No. 7,119,168, incorporated by reference herein in its entirety) provided data that showed that this 54-mer peptide caused paralysis and inhibited calcium uptake by two ovarian cancer cell lines (U.S. Pat. No. 7,273,850, incorporated by reference herein in its entirety). There remains a need for anti-cancer agents that do not have paralytic activity.
One group of calcium ion channels implicated in cancer is the Transient Receptor Potential (TRP) channels that are found across the invertebrates and vertebrates. A member of the TRP super-family was named after it was discovered that activates in the presence of vanilloids (capsaicin from hot peppers for example) and are called Transient Receptor Potential Vanilloid. The first four of these receptors tested (TRPV1, TRPV2, TRPV3 and TRPV4) all responded to capsaicin and were also responsible for detecting changes in temperature. The remaining two of the TRPV sub-family, TRPV5 and TRPV6 were found predominantly in epithelial type tissues and were responsible for influx of calcium ion. TRPV5/6 were identified as responsible for import of calcium into epithelial tissues of the intestine and hence uptake of calcium from the diet. These channels were also shown to be present in a number of other tissues in varying amounts, but most notably intestinal epithelial cell, kidney, placenta and pancreas. The expression of TRPV6 was measured as highly elevated in human ovarian, prostate and mammary cancer, thyroid and colon tumors and in some known prostate cancer cell-lines. In prostate cancer, TRPV6 was hugely up-regulated in carcinomas that have breached to tissue wall and have begun to metastasize (Zhuang et al. 2002). TRPV6 is therefore a potential target for cancer therapy. Accordingly, there is a strong need for compounds that block the activity of the overabundant TRPV6 channels in cancer cells.
More recently, the involvement of TRPV6 in cancer has been suggested to activate a pro-survival/anti-apoptotic pathway in two cancer cell lines with over-expressed TRPV6. In the prostate cancer cell line (LnCaP) intracellular calcium concentrations, increased by greater levels of TRPV6, activate nuclear factor of activated T-cells (NFAT; Lehen'kyi et al. 2007). Bolanz et al. (2008) have also shown the involvement of calcium-activated NFAT in switching on anti-apoptotic genes in a human breast cancer cell line (T 47-D). Bolanz et al. showed that reducing the production of TRPV6 by interfering RNA seemed to relieve the apoptotic block. These reports further accentuate the need for TRPV6 inhibitors in cancer treatment.